Heat stress assessment in artistic glass units

Accuracy of metabolic rate estimates from heart rate under heat stress-an empirical validation study concerning ISO 8996

The standard ISO 8996 provides methods for the determination of metabolic rate from measured oxygen consumption (M_VO2), as well as simplified estimation algorithms based on heart rate (M_HR). We quantified the accuracy of these methods by comparing M_HR with M_VO2 measured in 373 climatic chamber experiments under different workloads and widely varying heat stress conditions. While our results confirmed the 5% accuracy level for M_VO2, M_HR considerably overestimatedM_VO2 due to the rise in core temperature concomitantly increasing heart rate by approximately 30 bpm/°C resulting in an overall error of 43%. After individually correcting for this bias the accuracy was 10-15% as stipulated by the standard. Thus, methods correcting for the thermal component of heart rate, e.g. by introducing intermittent resting periods of sufficient length of at least five min when investigating heat stress at workplaces, should become a mandatory element in the ongoing revision of the relevant standards.

Globe Temperature and Its Measurement: Requirements and Limitations

This study addresses the measurement of the globe temperature. For this purpose, two globe thermometers with different diameters (50 and 150 mm) and a variety of thermal environmental conditions were considered. The assessments of the response times and of the influences of the globe diameter and the air velocity on the measured globe temperatures are discussed. The results of the response times clearly put in evidence that the values usually stated in the literature can be questioned and that longer measurement periods must be considered. In fact, response times >30 min were obtained in 68% of the tests performed. Moreover, differences >20ºC were obtained between the 150 and 50 mm sensors, highlighting the influence of the globe diameter. The analysis of the effect of the air velocity on the globe temperature shows mean relative differences >30% between tests in still air and with the higher air velocity considered (1.81 m s-1). On the basis of measurements carried out with the 50 mm globe, correction equations to the standard globe temperature for both natural and forced convection are proposed.